Hadron Suppression in DIS @HERMES

Pasquale Di Nezza(on behalf of the HERMES Collaboration)

•DF and FF modification in a nuclear medium•Nuclear attenuation measurements at HERMES•Comparison with theory•Hadron re-interaction vs partonic energy loss

Quark and Matter, Oakland Jan 11-17, 2004

DF and FF on Nucleon & Nuclear Medium

f

hfff zDdxqz )()()(d h

Inclusive DIS on nuclei: EMC effect

Interpretation at both hadronic (nucleon’s binding, Fermi motion, pions) and partonic levels (rescaling, multi-quark

system)

FF on nucleon:

DF and FF on Nucleon & Nuclear Medium

f

hfff zDdxqz )()()(d h

FFs are measured with good precision and follow pQCD evolution like DFs (HERMES: EPJ C21(2001) 599). What happens in a

nuclear medium ?

/νEz h

Nuclear AttenuationObservation: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction.

Nuclear Attenuation

Production and Formation Time measurements + FFs are crucial for the understanding of the space-time evolution of the

hadron formation process

Observation: reduction of multiplicity of fast hadrons due to both hard partonic and soft hadron interaction.

Df2f

hff

2f

Af2f

hff

2f

D

h2

DIS

A

h2

DISM

(x)qΣe(z)(x)DqΣe

(x)qΣe(z)(x)DqΣe

dzdνσd

σ1

dzdνσd

σ1

υ)(z,R

The energy range is well suited to study quark propagation and hadronizationMeasurements over the full z rangePossibility to use several different gas targetsPId: +, -, 0, K+, K-, p, p-

HERMES @ DESYIt is an experiment which studies the spin structure of the nucleon … and not only …

•27.5 GeV e+, Ie~40 mA

Last part of the fill dedicated to high-density unpolarised target runs:

The Internal Target(NIM A343 (1994) 334)

•Internal storage cell•Pure gas target, no dilution factor•Nuclear targets: (H, D), 3He, 4He, 14N, 20Ne, 40Ar, 84Kr, 131Xe•Densities: ~1015 – 1017 nucl*cm-2

The Spectrometer

•e+ identification: 99% efficiency and <1% of contamination•PID: RICH, TRD, Preshower, e.m. Calorimeter•For N target: by Cerenkov pion ID in the range 4<p<14 GeV•For He, Ne, Kr target: by RICH , K, p ID in the range 2.5<p<15 GeV

(NIM A417 (1998) 230)

Particle Identification

Positron – hadrons separation:

Double radiator RICH: Aerogel + C4F10. Cerenkov photons detected by ~4000 PMTs.Detection efficiency: 99% (), 90% (K), 85-95% (p)

Hadron Attenuation

•Clear nuclear attenuation effect•Increase with consistent with EMC data at higher energy•Discrepancy with SLAC due to the EMC effect, not taken into account at that time•HERMES kinematics is well suited to study quark propagation and hadronization

Hadron AttenuationEMC

SLAC

•Significant attenuation of fast forward hadrons•HERMES data provide information in the unexplored region z>0.8

HERMES

Hadron separation vs HERMES, PLB 577 (2003) 37

HERMES, PLB 577 (2003) 37

Hadron separation vs

Experimental findings:

+ = - = 0 ~ K-

K+ > K-

p > p, p > , p > K-

HERMES, PLB 577 (2003) 37

Hadron separation vs

Hadron separation vs z

Different FF modification for quark and anti-quark

Different h for mesons and baryons

Different h:+ = - 20 mb+ 17 mb, - 23 mbp 40 mb, p- 60 mb

HERMES, PLB 577 (2003) 37

Nuclear Attenuation on He, Ne, Kr

Large effect as a function of the atomic mass number

Assuming the dependence:A = 1-Rh

att

Data suggest ~2/3

Nuclear Attenuation on He, Ne, Kr

Nuclear Attenuation vs Q2

Dependence on Q2: stronger at small , weaker at high

Pt dependenceIn pA collisions the p gains extra transverse momentum due to random soft collisions. Partons enter the final hard process with extra kt (Cronin eff.)

Multiple parton scattering effects become dominant at pt~ 1-2 GeV

pA = A(pt)pp CERNRHIC

PHENIX

Data show a pt enhancement similar to that observed in pA scattering (Cronin effect)

The hard component of incoherent parton scattering becomes dominant at pt~1-2 GeV

Pt dependenceIn DIS neither multiple scattering of the incident particle nor interaction of its constituents complicate the interpretation

Clean and reliable information on quark transport in ‘cold’ nuclear matter

XN Wang Parton en

lossInduced

rad

Comparison with Theory

B Kopeliovich

Ind radiationh rescatt

A Accardi Q2 rescaling

Nucl absorbion

F ArleoFF

modificationenergy change

T FalterFSI

Transport model

BialasGyulassy

Formation Time

0

2h

2hh/q

)Q,zdtW(t,

)Q,(zD~

Gluon Bremsstrahlung B.Kopeliovich et al., hep-ph/9511214hep-ph/0311220

FF modification: Nuclear Suppression + Induced Radiation

•Vacuum energy loss: qgq’. (dE/dz ~2.5 GeV/fm by E772/E866 for DY on nuclei)•Energy loss induced by multiple interactions in the medium (rising in pt)•Color Transparency of the qq (~1/Q2)

Gluon BremsstrahlungB.Kopeliovich et al., hep-ph/9511214hep-ph/0311220

Fast pions are consistent with GB model (production length lp(1-zh)/Q2 vanish at zh 1)

Nuclear SuppressionNuclear Suppression + Induced

Radiation

Gluon BremsstrahlungB.Kopeliovich et al., hep-ph/9511214hep-ph/0311220

Only prediction for h containing target valence quark.

Good agreement also for K+

Gluon BremsstrahlungB.Kopeliovich et al., hep-ph/9511214hep-ph/0311220

Combined effects: •pre-hadron shrinks at large Q2

•larger nuclear transparency•production lengths contracts

Good description; Faster rise at high Pt ?

FF and their QCD evolution are described in the framework of multiple parton scattering (DGLAP).

•The emitted g and the leading q propagate coherently Landau-Pomeranchuk-Midgal interference effects. •Different modification of quark and antiquark FF.

Rescattering without gluon radiation: pt-broadening.

Rescattering with another q : mix of q and g FF.

g-rescattering including g-radiation: dominant contribution in QCD evolution of FF.

FF modification X.N.Wang et al.,

NPA696(2001)788PRL89(2002)162301

FF modification (parton energy loss)

•1 free parameter tuned on 14N (quark-gluon correlation strength inside nuclei)

•dE/dx for HERMES dE/dx for PHENIX (Au)

X.N.Wang et al., NPA696(2001)788

PRL89(2002)162301

Gluon Density0A0A0staexp R2)/R2(EE

•Cold <--> Hot nuclear matter correlation

•Gluon density in Au+Au~15 times higher than in cold matter

X.N.Wang et al., NPA696(2001)788

PRL89(2002)162301

Nice agreement for p+, p-, K+ with Q2-rescaling + nuclear absorption (lower curves).

Rescaling + Absorption Model

))Q(Q(z,D)Q(z,D

))Q(Q(x,q)Q(x,q

)(Q;

22A

hf

2A|hf

22Af

2Af

)()(

2A

2N2

ANA

2s

2As

QA.Accardi et al.,

NPA720(2003)131

(Pre-)Hadron FSI and formation times

RM is very sensitive to the pre-h ; (pre-h=0.33 h)f>0.5 fm/c compatible with data

T.Falter et al., nucl-th/0303011

FF modification + transport coef.F.Arleo et al.,

NPA715(2003)899

•Energy loss taken into account

•Soft gluons radiated in the dense QCD medium (transport coefficient calculated from DY)

•Nice agreement with both HERMES and old EMC data

With formation time effect

Without formation time effect

Disentangling absorption and induced energy loss

In case of absorption, suppression for double-hadron production is SMALL compared to single-hadron

production

D

1h

2hA

1h

2h

2

RR

RR

R

Could it be too naïve ?

R2 depends on:•hadron production length •local nuclear density•absorption cross section•Pt, z1, z2, …

Disentangling absorption and induced energy loss

Preliminary R2 calculated for Kr/D and N/D:• >7 GeV, Eh>1.4 GeV, zleading>0.5• opposite charges neglected (rank-2)

R2(Kr/D) = 0.929 ± 0.025

R2(N/D) = 0.946 ± 0.018

Results from STAR show jet suppression is due to FSI (energy loss). No contribution from absorption …

Disentangling absorption and induced energy loss

Preliminary R2 calculated for Kr/D and N/D:• >7 GeV, Eh>1.4 GeV, zleading>0.5• opposite charges neglected (rank-2)

R2(Kr/D) = 0.929 ± 0.025

R2(N/D) = 0.946 ± 0.018

Results from STAR show jet suppression is due to FSI (energy loss). No contribution from absorption … high Pt events, different zh distributions. It’s difficult to compare HERMES-RHIC … for the moment.

Pre-hadronic re-interaction and/or partonic energy loss ?

ConclusionsConclusionsSignificant hadron suppression, in a wide region of the kinematical plane, measured for 4He, 14N, 20Ne, 84Kr

Pasquale Di Nezza

First observation of hadron-type dependence of the attenuation: +, -, 0, K+, K-, p, p-Large atomic mass number dependenceThe Cronin effect has been observed: transition occurs at Pt~1 GeVLarge final hadron re-interaction is unlikely

Outlook: Disentangle between and z dependence Pt broadening for different hadrons Double/Single-hadron ratio

GOALTo obtain unambiguous information on hadron formation

and transport in Cold Nuclear Matter

Hadrons and Pions @ Ebeam=12 & 27 GeV

Extension of the range down to 2 GeV